Wide angle lens system having a distorted intermediate image

ABSTRACT

The wide angle lens system described herein allows projection devices (e.g., rear projection display devices) to be more compact than would otherwise be possible. The lens system includes a wide angle lens stage and a relay lens stage. When operating as a projection device, the relay lens stage projects a distorted intermediate image to the wide angle lens stage, which projects the image for display. The distortion cause by the relay lens stage compensates (i.e., is approximately equal and opposite) for the distortion caused by the wide angle stage. The distortion can be the image shape and/or the focal plane. When operating as a taking device, the wide angle stage provides a distorted image to the relay lens stage, which compensates for the distortion and provide a less distorted, or even non-distorted image, for capture.

RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.10/222,050, filed Aug. 16, 2002 now U.S. Pat. No. 7,009,765. Theentirety of the above named application is herein incorporated byreference for all purposes.

TECHNICAL FIELD

The invention relates to lenses for use in optical devices. Moreparticularly, the invention relates to lenses for use in optical devicesemploying wide angle lens systems.

BACKGROUND

In order to provide a television with a screen size greater thanapproximately 40 inches a display device other than a direct viewcathode ray tube (CRT) is typically used. As the screen size of a CRTincreases, so too does the depth. It is generally accepted that forscreen sizes greater than 40 inches direct view CRTs are no longerpractical. Two alternatives exist for large screen (>40 inch screensize) displays: projection displays and plasma displays.

Current plasma displays are much more expensive than projectiondisplays. Plasma displays are generally thin enough to mount on a wall,but can be heavy enough that mounting can be difficult. For example,current 42 inch plasma displays can weigh 80 pounds or more and 60 inchplasma displays can weigh 150 pounds or more. One advantage of plasmadisplays over current projection displays is that plasma displays aretypically much thinner than current projection displays having the samescreen size.

Projection displays, specifically rear projection displays, aretypically more cost-effective then plasma displays. Projection displaysmay also consume too much space in a room to provide a practicalsolution for large screen needs. For example, typical 60 inch rearprojection displays are 24 inches thick and can weigh 200 to 300 pounds.

FIG. 1 illustrates a prior art rear projection display device. Ingeneral, display device 100 includes optical engine 140, projection lens130, back plate mirror 120 and screen 110. Optical engine 140 generatesan image to be projected on screen 110. projection lens 130 projects theimage from optical engine 140 on to back plate mirror 120, whichreflects the image to screen 110. The size of display device 100 isproportional to the size of the image to be displayed on screen 110.Thus, for large screen sizes (e.g., >60 inches), the overall size ofdisplay device 100 can be very large.

Thin rear projection display devices have been developed that are lessthan 12 inches thick. However, these thinner rear projection displaydevices typically rely on an aspherical mirror, which is difficult tomanufacture and difficult to align. The difficulties associated with theaspherical mirror results in current thin rear projection displays beingexpensive, which restricts the availability of rear projection displaysin desirable packages.

FIG. 2 illustrates a prior art thin rear projection display device withan aspherical mirror. An image from optical engine 260 is projected onreflective mirror 240 by projection lens 250. Reflective mirror 240reflects the image to aspherical mirror 230, which magnifies theprojected image and extends the field ray angle. Aspherical mirror 230reflects the image to back plate mirror 220, which then reflects theimage to screen 210. While rear projection display device 200 provides athinner package for the same size screen as compared to display device100 of FIG. 1, the manufacturing and alignment issues associated withuse of aspherical mirror 230 greatly increases the cost of displaydevice 200.

Another shortcoming of display device 200 is the angle of optical engine260 with respect to mirrors 220, 230 and 240 and to screen 210. Withoutcompensation, the angle of optical engine 260 results in a trapezoidal,or keystone, shaped image. The compensation associated with the angle toprovide a square image further increases the cost and complexity ofdisplay device 200.

SUMMARY

In one embodiment, a lens system includes a first stage to create adistorted intermediate image and a second, wide angle lens stage thatcauses distortion to substantially cancel the distortion of theintermediate image and to project a substantially non-distorted imagecorresponding to the intermediate image.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is illustrated by way of example, and not by way oflimitation, in the figures of the accompanying drawings in which likereference numerals refer to similar elements.

FIG. 1 illustrates a prior art rear projection display device.

FIG. 2 illustrates a prior art thin rear projection display device withan aspherical mirror.

FIG. 3 illustrates one embodiment of an ultra-thin rear projectiondisplay device with planar mirrors parallel to a screen.

FIG. 4 illustrates one embodiment of a folded wide angle lens systemhaving a distorted intermediate image.

FIG. 5 illustrates one embodiment of a wide angle lens system having adistorted intermediate image.

FIG. 6 illustrates one embodiment of a rear projection display devicewith a wide angle lens system having an intermediate image.

DETAILED DESCRIPTION

Wide angle lens systems having a distorted intermediate image aredescribed. In the following description, for purposes of explanation,numerous specific details are set forth in order to provide a thoroughunderstanding of the invention. It will be apparent, however, to oneskilled in the art that the invention can be practiced without thesespecific details. In other instances, structures and devices are shownin block diagram form in order to avoid obscuring the invention.

The wide angle lens system described herein allows projection devices(e.g., rear projection display devices) to be more compact than wouldotherwise be possible. The lens system includes a wide angle lens stageand a relay lens stage. When operating as a projection device, the relaylens stage projects a distorted intermediate image to the wide anglelens stage, which projects the image for display. The distortion causedby the relay lens stage compensates (i.e., is approximately equal andopposite) for the distortion caused by the wide angle stage. Thedistortion can be to the image shape and/or the focal plane. Whenoperating as a taking device, the wide angle stage provides a distortedimage to the relay lens stage, which compensates for the distortion andprovides a less distorted, or even non-distorted image, for capture.

FIG. 3 illustrates one embodiment of a rear projection display devicewith planar mirrors parallel to a screen. As described in greater detailbelow, use of planar mirrors parallel to the screen as well as a wideangle projection lens having an optic axis that is perpendicular to themirrors and the screen allows the rear projection display device to bethinner and simpler than prior art rear projection display devices. Forexample, an ultra-thin rear projection display device as describedherein that is less than 7 inches thick can provide a 60 inch image.

In one embodiment, rear projection display device 300 includes screen310, back plate mirror 320, intermediate mirror 330, lens system 340 anddigital micromirror device (DMD) 350. Other components known in the artare not illustrated for reasons of simplicity of description. An imagecan be provided to DMD 350 in any manner known in the art. DMD 350selectively reflects light from a light source (not shown in FIG. 3) tolens system 340. Any type of display device known in the art can be usedin display device 300. Other types of devices (e.g.,microelectromechanical systems (MEMS), grating light valve (GLV), liquidcrystal display (LCD), liquid crystal on silicon (LCOS)) can be used toprovide an image to lens system 340.

In one embodiment, DMD 350 is offset from the optic axis of lens system340 such that only a portion (e.g., 50%, 60%, 40%) of the available lensfield is used. By offsetting DMD 350 with respect to the optic axis oflens system 340, the image from DMD 350 is projected by lens system 340in the upper portion of the lens field to intermediate mirror 330.Alternatively, a lower portion of the lens field can be used to projectan image to intermediate mirror 330. In such an embodiment, lens system340 would be above intermediate mirror 330, which would be above backplate mirror 320.

In order to project an image as described, lens system 340 is a verywide angle lens system. In one embodiment, lens system 340 has a fieldangle of 152° or more; however, other lenses can be used. In general,the wider the angle of lens system 340, the thinner display device 300can be made. Description of a suitable wide angle lens system isdescribed in greater detail below.

Intermediate mirror 330 reflects the image to back plate mirror 320,which reflects the image to screen 310, which can be, for example, aFresnel lens. Back plate mirror 320 is also a planar mirror and isparallel to screen 310 and perpendicular to the optic axis of lenssystem 340. Because the optic axis of lens system 340 is perpendicularto intermediate mirror 330 and both intermediate mirror 330 and backplate mirror 320 are planar and parallel to screen 310, the distortioncaused by angled lenses and aspherical mirrors is absent in displaydevice 300. This simplifies the design of display device 300 and reducesthe cost and complexity of manufacturing. Embodiments of a rearprojection display device in which the wide angle lens system describedherein can be used is described in greater detail in theabove-referenced patent application, which is incorporated by reference.

FIG. 4 illustrates one embodiment of a folded wide angle lens systemhaving a distorted intermediate image. While the lens system of FIG. 4is described as a projection lens system, the lens system can also beused for image capture, for example, by a camera.

DMD 410 provides an image to the lens system. As described above, othertypes of devices can be used to provide an image to the lens system.Prism 420 directs the image to relay lens group 430. Relay lens group430 projects the image from prism 420 to prism 440 and distorts theimage such that intermediate prism 440 receives an intentionallydistorted intermediate image, where images of objects near the edge ofthe field are compressed in the radial direction.

In one embodiment, relay lens group 430 includes 9 lenses; however, anynumber of lenses can be used based on, for example, the desireddistortion of the intermediate image, or the overall size of the lenssystem. The distortion to be caused by relay lens group 430 is equal andopposite the distortion caused by wide angle lens group 450. In oneembodiment, the intermediate image is approximately a half circle imagein a warped image plane. In alternate embodiments, other types ofdistortion can be used. For example, if the full lens field is to beused, the distorted intermediate image would be a generally circularimage. The image plane may or may not be warped.

Intermediate prism 440 provides a 90° fold of the image path. Asdescribed below with respect to FIG. 5, the fold is not required.Alternatively, other fold angles, for example, 45°, 30°, 135° could beused. Wide angle lens group 450 projects the distorted intermediateimage to a screen for display. Because wide angle lens group 450 causesdistortion to the image to be projected and the intermediate image hasbeen pre-distorted by relay lens group 430, the resulting imageprojected by the lens system has little or no distortion. In oneembodiment, the total distortion caused by relay lens group 430, wideangle lens group 450 and any associated prisms is less than 3%.

In one embodiment, the optic axes of the lenses of relay lens group 430are aligned. Similarly, the optic axes of the lenses of wide angle lensgroup 450 are also aligned. Wide angle lens group provides a field angleof greater than 100°. In one embodiment the field angle is 153°;however, any angle can be provided. In one embodiment, the optical axisof wide angle lens group 450 is perpendicular to the screen so thatkeystone, or trapezoidal, distortion is absent.

FIG. 5 illustrates one embodiment of a wide angle lens system having adistorted intermediate image. The lens system of FIG. 5 is similar tothe lens system of FIG. 4 except that the lens system of FIG. 5 is notfolded. That is, wide angle lens system 450 is co-axial with relay lenssystem 430. The lens system of FIG. 5 does not include an intermediateprism. An intermediate prism can be included, if desired.

In one embodiment, the lens system of FIG. 5 has the followingprescription:

Surface RDY THI RMD GLA  1: 46.74531 4.000000 NBF1_HOYA  2: 28.811635.051213  3: 30.58292 4.000000 NBFD10_HOYA  4: 21.01576 8.441106  5:129.13928 4.000000 SLAM60_OHARA ASP: K: 0.000000 IC: YES CUF: 0.000000A: 0.664982E−04 B: −.187975E−06 C: 0.420794E−09 D: −.348519E−12  6:21.14941 8.859193 ASP: K: 0.000000 IC: YES CUF: 0.000000 A: −.367450E−04B: 0.130594E−06 C: −.665374E−09 D: 0.794813E−12  7: 78.00018 3.124861FDS90_HOYA  8: 16.67079 9.473114 BACD16_HOYA  9: −13.03245 0.200000 10:−17.74399 6.650512 MNBF1_HOYA ASP: K: 0.000000 IC: YES CUF: 0.000000 A:0.314557E−03 B: −.254460E−05 C: 0.149709E−07 D: −.573297E−10 11:−14.40905 0.200000 ASP: K: 0.000000 IC: YES CUF: 0.000000 A:−.440469E−04 B: 0.237538E−05 C: −.134637E−07 D: 0.222969E−10 12:131.97096 6.000000 MNBF1_HOYA ASP: K: 0.000000 IC: YES CUF: 0.000000 A:0.711368E−04 B: −.624364E−06 C: 0.210000E−08 D: −.350000E−11 13:−15.59413 2.000000 ASP: K: 0.000000 IC: YES CUF: 0.000000 A:0.257396E−03 B: −.884746E−06 C: 0.186450E−08 D: 0.216077E−11 14:INFINITY 30.000000  FD60_HOYA 15: INFINITY 24.565488  16: −64.356374.999034 FD60_HOYA 17: −1966.99974 5.494742 18: −96.81620 16.104081 NBFD13_HOYA 19: −39.51766 0.200000 20: 136.11245 14.269098  LAC8_HOYA21: −114.50422 39.301091  22: −250.53752 5.915028 BACD16_HOYA 23:−62.97973 24.296450  STO: 8.12022 3.000000 FDS90_HOYA 25: 7.275122.000000 26: −67.85690 5.522870 BACD16_HOYA 27: −5.88750 7.902370FDS90_HOYA 28: 135.96725 1.688647 29: −35.98083 10.637917  MNBF1_HOYAASP: K: 0.000000 IC: YES CUF: 0.000000 A: 0.956626E−04 B: 0.298084E−06C: −.100781E−07 D: 0.371253E−10 30: −16.84259 0.200000 ASP: K: 0.000000IC: YES CUF: 0.000000 A: 0.434637E−04 B: 0.131005E−06 C: −.120433E−08 D:0.718134E−12 31: 29.02346 8.028674 SLAH60_OHARA ASP: K: 0.000000 IC: YESCUF: 0.000000 A: 0.696210E−05 B: −.847612E−07 C: 0.104328E−09 D:−.182720E−12 32: 186.81664 4.000000 ASP: K: 0.000000 IC: YES CUF:0.000000 A: −.196461E−05 B: 0.343490E−07 C: −.146991E−09 D: 0.000000E+0033: INFINITY 21.000000  BSC7_HOYA 34: INFINITY 2.000000 35: INFINITY3.000000 FC5_HOYA 36: INFINITY 0.440000In the above prescription, surfaces 1-13 correspond to wide angle lensgroup 450 and surfaces 16-32 correspond to relay lens group 430. Inalternate embodiments, other prescriptions and/or other materials canalso be used.

FIG. 6 illustrates one embodiment of a rear projection display devicehaving a wide angle lens. Display device 600 includes screen 610, wideangle lens system 620 and DMD 630. In one embodiment, screen 610 is aFresnel lens as described in greater detail in the related applicationreferenced above, which is incorporated by reference herein.

An image is generated a provided by optical engine components (not shownin FIG. 6) that are known in the art and directed to wide angle lenssystem 620 via DMD 630. In alternate embodiments, DMD 630 can bereplaced by other components, for example, microelectromechanicalsystems (MEMS), grating light valves (GLV), liquid crystal display(LCD), liquid crystal on silicon (LCOS), etc. The optic axis of DMD 630is aligned with the optic axis of wide angle lens system 620 so that thefull lens field is used to project the image to screen 610.

As described herein, an image is projected on a screen through a wideangle lens system. The screen can be a Fresnel lens. However, many otherobjects can operate as a screen for purposes of displaying an image. Ingeneral, any object that diffuses light can be used as a screen. Forexample, a wall, water or fog can be used as a screen.

Reference in the specification to “one embodiment” or “an embodiment”means that a particular feature, structure, or characteristic describedin connection with the embodiment is included in at least one embodimentof the invention. The appearances of the phrase “in one embodiment” invarious places in the specification are not necessarily all referring tothe same embodiment.

In the foregoing specification, the invention has been described withreference to specific embodiments thereof. It will, however, be evidentthat various modifications and changes can be made thereto withoutdeparting from the broader spirit and scope of the invention. Thespecification and drawings are, accordingly, to be regarded in anillustrative rather than a restrictive sense.

1. An apparatus comprising: an image capture device; a wide angle lensstage including a wide angle lens with a field angle greater than 100°to create an intermediate image with substantial wide angle distortionwhere the images of objects near the edge of the field are compressed inthe radial direction; and a relay lens stage that causes distortion tosubstantially cancel distortion of the intermediate image and to projecta substantially non-distorted image corresponding to the intermediateimage to the image capture device.
 2. The apparatus of claim 1, whereinthe relay lens stage and the wide angle lens stage are co-axial.
 3. Theapparatus of claim 1, wherein an optic axis of the wide angle lens stageand an optic axis of the relay lens stage form an angle.
 4. Theapparatus of claim 3, wherein the angle is approximately 90°.
 5. Theapparatus of claim 3, wherein the angle is substantially less than 90°.6. The apparatus of claim 3, wherein the angle is substantially greaterthan 90°.
 7. The apparatus of claim 1, wherein the substantiallynon-distorted image has less than 3% distortion.
 8. The apparatus ofclaim 1, wherein the intermediate image is a generally circular image.9. The apparatus of claim 8, wherein the intermediate image isapproximately a half circle image.
 10. The apparatus of claim 1, whereinthe intermediate image is in a warped image plane.
 11. A cameracomprising: a wide angle lens stage including a wide angle lens with afield angle greater than 100° to create an intermediate image with wideangle distortion and substantially no trapezoidal distortion; and arelay lens stage that causes distortion to substantially cancel the wideangle distortion of the intermediate image and to provide asubstantially non-distorted image for image capture.
 12. The camera ofclaim 11, wherein the relay lens stage and the wide angle lens stage areco-axial.
 13. The camera of claim 11 wherein an optic axis of the wideangle lens stage and an optic axis of the relay lens stage form anangle.
 14. The camera of claim 13, wherein the angle consists of one ofapproximately 90°, substantially greater than 90°, and substantiallyless than 90°.
 15. The camera of claim 1, wherein the intermediate imageis a generally circular image.
 16. The camera of claim 15, wherein theintermediate image is approximately a half circle image.
 17. A lenssystem for an image taking device comprising: a wide angle lens stageproviding a field of at least 100° to generate a distorted intermediateimage, wherein the distorted intermediate image is a generally circularimage; and a second lens stage to substantially cancel distortion of theintermediate image to generate a substantially non-distorted image forimage capture.
 18. The lens system of claim 17, wherein the second lensstage and the wide angle lens stage are co-axial.
 19. The lens system ofclaim 17, wherein an optic axis of the wide angle lens stage and anoptic axis of the second lens stage form an angle.
 20. The image takingdevice of claim 1, wherein the substantially non-distorted image hasless than 3% distortion.